Special interest automobiles are often sought after as distinctive transportation as well as for collection or show purposes. An owner who drives such an automobile, particularly a vintage or classic sports car, does so for pleasure, but will often find the experience to be compromised by mental comparisons to contemporary, more sophisticated vehicles. Some aspects of the experience may be cherished for their differences but, insofar as transmission performance and ease of gear-selection, the only satisfaction may be in the ability to cope with the limitations of obsolete equipment.
Modification of these autos is frowned upon by most enthusiasts, who place great value on originality. Engine “swapping”, or converting to a different type engine, is particularly distasteful to the purist and will usually devalue the automobile severely. Transmission conversions are not viewed as negatively, perhaps because the transmission is buried beneath the automobile so that the change is not as obvious as an engine conversion. In fact, this change is not at all objectionable if it does not entail any alterations to the car itself. Thus, if it is readily possible to return an automobile to its original state, or give the original transmission, with an unaltered vehicle to a new owner, so as to convey the sanctity of “original parts”, a transmission conversion is seen as a case of “no harm, no foul”. Theoretically, the less drastic the required alterations, the more acceptable will be the conversion, but purists are indeed purists and tend to be quite arbitrary in matters of “originality”. This is the downfall of most otherwise desirable transmission conversions. If the replacement transmission has the virtue of being more robust, it is probably more bulky, so that the transmission cover, floor and/or frame of the car require alteration to provide the needed clearance. If the replacement transmission provides additional speed ranges, such as a modern five-speed, for installation in place of one with three or four speeds, it is almost certain to be significantly longer. This will dictate that the drive shaft be shortened and/or a cross-member be altered. Other problems arise in the form of incompatible transmission mounting styles, necessitating frame alterations, or a different gear-shift lever location, requiring that the transmission cover be altered, either of which makes the change obvious. Other problems, such as an incompatible speedometer drive make such a conversion less desirable. As a typical example, XKE JAGUAR automobiles, made from 1961 through 1974, are highly prized by enthusiasts and collectors. Many of these cars are still in use, particularly on special occasions such as club events. The XKE transmissions are four-speed units originally designed in the 1930's and somewhat improved, but not capable of the smooth, nearly effortless gear changes of state-of-the-art designs. Moreover, the standard JAGUAR ratios require engine speeds of around 3,500 revolutions per minute or so at common road speeds of 70-75 mph. A five-speed transmission is almost certain to be significantly longer, from front flange to output coupling, than the original four-speed transmission to be replaced. The TREMEC five-speed transmission, originally designed for the FORD MUSTANG, has a case that is 9¼″ in length and a tailshaft housing that is 15″ long, so that the transmission length is 24½″. The TREMEC transmission houses the first through fourth-speed gears in the case, while the fifth-speed gears are contained in the tailshaft housing. The four-speed JAGUAR transmission case is 10¼″ long and the tailshaft housing adds another 3″, for a transmission length of 13¼″.
Such conversions are done as custom installations by garages or shops that cater to special interest automobiles. Thus, transmission conversions are often produced as an individual effort, or in very low volume, by technicians of ordinary skill in the mechanical arts. No more than ordinary skill is required to make a shorter tail shaft and tail shaft housing, so as to reduce the TREMEC transmission length to 16¼″ but, any greater reduction threatens transmission operability. To further compound the problem, the usual manner of adapting the bolt pattern of a “transplanted” transmission to an original clutch housing is by means of a ⅝″ or ¾″ thick adapter plate, having both the original and new bolt patterns. This further adds to the driveline length of the conversion. When this is considered, it is seen that a typical effective overall assembly length is actually closer to 17 inches. Thus, the available XKE five-speed conversions require many of the aforesaid alterations and do not replace the original transmission, except with vehicle alterations.
A first object of the present invention is therefore, to provide a competent, five-speed transmission conversion for XKE JAGUARS and other special interest automobiles. A second object is to provide this conversion in a form that does not compromise the originality of the subject vehicle. Yet a third object of the inventions is to provide this conversion in a form that will interchange with the original transmission, for purposes of ease of installation and economy.